Waterjet propulsion has many benefits over propeller propulsion of marine vessels. The main benefit is one of safety, having no protrusions below the hull. Another benefit is the better maneuverability of the vessel because waterjets have the capability to direct the jet thrust in any direction. Steering and reversing is effected by deflecting the jet stream to either side through the use of deflecting baffles or by turning an articulating nozzle left or right. In both cases, the flow direction of the jet stream results in vessel directional change. Such baffles or articulating nozzles pivot about a vertical axis, and the pivots are supported by a diffuser, fixed to the pump, that ducts the jet flow from the pump to the nozzle.
Reverse operation of the vessel is obtained by re-directing the jet stream generally forward and underneath the vessel by the use of a reverse gate that pivots about a horizontal axis and deflects the jet flow. In one approach to provide reverse thrust and steering, made popular by C.W.F Hamilton and Company of New Zealand, the pivots of the reverse gate (also referred to as a reverse bucket) are supported by the diffuser. The reverse gate stops the rearward direction of the jet stream and through ducts provided in the reverse gate, sending the water forward and underneath the vessel, thereby causing the vessel to move in reverse. The steering deflector or steering nozzle is placed in such a way, that, while in reverse, the response will be opposite to that of a rudder steered vessel, causing confusion for the experienced mariner. Neutral is obtained by dropping the reverse gate half way down so that the upper portion of the water stream is reversed and the lower portion remains untouched, balancing forward and reverse flows. Turning the steering wheel in either direction causes the vessel to rotate in place since the resultant effect of the balanced forces is a sideways force on the stern. This is referred to as zero-speed steering and is considered a desirable feature, enhancing maneuverability of waterjet-powered vessels.
A second approach for steering and reversing waterjet-powered vessels can be seen in U.S. Pat. No. 5,304,078 (Kaneko) entitled “REVERSE THRUST BUCKET FOR JET DEVICE.” In this approach, the reverse gate pivots are attached to the steering nozzle, and the nozzle is provided with a reverse water flow outlet underneath the nozzle, so that when the jet stream is cut by the dropping reverse gate, the water is re-directed through this outlet and expelled below the vessel and forward, creating a reverse response. Articulating the steering nozzle will produce steering response in the conventional way identical to rudder steered vessels. In this method however, no steering response in neutral is obtained since forward and reverse water flows balance no matter what steering direction is selected. Another disadvantage of the second reverse method is that the reversing system deflects the reverse water flow directly into the waterjet intake, aerating the waterjet pump and rendering the waterjet and the steering and reverse response less effective.
The instant invention combines the advantages of the zero-speed steering of the first approach with the advantages of conventional reverse response of the second approach while avoiding the disadvantages of both approaches.